On the topic of races:
More races is fun, and here's the ticket: they don't need to undergo a huge investment to do them! Worgen and Goblin starting areas--really cool, really memorable, but a big dump of resources that they don't have to focus on. Instead, take races already in place, give them some starter quests, then shove 'em out into the new world.
Horde: Ogres. Just freakin' do it finally, after all this time. The models are fine, the lore is rich, and there already exists a faction of Ogres within the Horde to justify their presence--the Stonemaul clan. Like the Darkspear Trolls, they don't represent the entire intricacies of the race but are enough of an off-shoot to work. Get them in, they suddenly become the biggest racial model ever ruining doorways everywhere, and the Horde goes back to its roots with another brutish race. Big money, big Ogre women.
Alliance: High elves. Exactly the same situation with the Ogres--the models exist (blue eyes instead of green!), the story setup is there (the Silver Covenant, Vereesa Windrunner), and it would probably take even less work than the Horde. I know it's a little cheaty what with Blood Elves already existing, but the premise isn't, especially if you consider how Pandaren exist as both Ally and Horde. Plus, you go back to the Alliance's roots of having a pretty and human-like race again, where as the past 2 times they've gotten goats and wolves.
Ethereal: Now, because folks might be a little underwhelmed with yet more ogres and elves, the next step is to create a third neutral faction in which players pick their allegiance (ala Pandaren). Thus, Ethereals; a cool-looking, unique foreign race. Most fans have been clamoring for their adoption since BC. But since lore-wise Ethereals don't really fall solidly into either Alliance or Horde camps, having them start out as neutral allows everybody to pick and choose to their liking. The race is no stranger to magics, weapon-wielding, summoning... they could fit plenty of current class archetypes. And given their nethery appearance and proclivity for money, trade, and bartering, I'm sure Blizz could come up with some especially neat racial abilities.
Naga: Psssh, Naga plz.
Race off-shoots: Like Taunkas, undead elves, brown ogres, forest trolls, dark iron dwarves... I like it. Only thing is, does it count as separate or simply a barber shop aesthetic that can be changed on the fly?